Hi. My name is Rick. I'm a camera repair technician with over 20 years in the business and I'll be glad to help you with your question today.
It shouldn't be too difficult as long as you get everything aligned correctly. The A/M switch usually has 2 things that will need to align with the change-over mechanism in the lens. There should be a metal tab on the back of the switch which fits into a slot on the lens mechanism to raise and lower a gear to engage and disengage the AF mechanism. In addition to this, there should be a notched metal piece on the back of the switch and to the side that engages an electronic, 2 position switch that tells the camera the lens is in the manual or auto mode. Both of these must be in the same position when the A/M switch is installed, (usually the A position). Once everything is aligned correctly you can secure the switch plate in place with a little glue. I use a strong contact cement but a little Super Glue will due.